Where does “kup-” come from?

kup- (Proto-Balto-Slavic) comes from Proto-Indo-European kwep- — to smoke, to steam; to boil; aroma, strong odor.

Ancestry of “kup-”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	kwep-	to smoke, to steam; to boil; aroma, strong odor

kup- — Etymology, Origin & Word History | Etymology Explorer